The present invention concerns a heat conductive molded part (heat conductive mold) of good heat conductivity and manufacturing method thereof
Recently, measures against the heat generated from electronic apparatuses are becoming an important issue by the high density implementation of semi-conductor package or higher integration and speed-up of LSI, following the performance enhancement, miniaturization, and weight reduction of electronic apparatuses. Ordinarily, in order to dissipate heat from heating devices, method to use printed circuit boards made of good heat conductive metals or ceramics, method to form a thermal veer hole to radiate heat in the substrate, method to use good heat conductive metals, ceramics or resins as semiconductor package material, method to interpose highly heat conductive grease or flexible heat conductive rubber sheet for the purpose of reducing the contact heat resistance between the heat source and the radiator, or between the heat source and the metallic heat conductive plate, method to use cooling fan, heat pipe or heat dissipation plate, or others are publicly known.
As such heat conductive mold requiring good thermal conductivity, molds filled with highly heat conductive aluminum oxide, boron nitride, aluminum nitride, magnesium oxide, zinc oxide, silicon carbide, quartz, aluminum hydroxide or other metal oxides, metal nitrides, metal carbides, metal hydroxides or other electric insulation fillers are used in practice.
However, the manufacturing method illustrated in the Japanese Patent Publication SHOU 62-154410 requires ultrasonic commotion machine or other special equipment or treatment processes, or use of specific boron nitride powder making the method inconvenient.
All of methods disclosed in the Japanese Patent Publication HEI 3-1 51 6 5 8, Japanese Patent Publication HEI 8-2 4 4 0 9 4, Japanese Patent Publication HEI 1 1-77795 and Japanese Patent Publication HEI 1 1-1 56 914 use flake form boron nitride powder or the like, require dies of complicated structure or extrusion molding equipment and complicated processing operations, and they were not necessarily simple manufacturing methods.
On the other hand, the Japanese Patent Publication Laid-Open No. HEI 1 1-87483 by the Applicant orients diamagnetic filler of 20Weight/mxc2x7K or more in thermal conductivity in a constant direction in polymer; however, boron nitride powder was not taken into account as diamagnetic material.
To solve these problems, we have studied seriously and found that a heat conductive mold characterized by that boron nitride powder is field oriented in a constant direction in polymer presents a good heat conductivity, a method to manufacture easily a heat conductive mold of good thermal conductivity applying the nature of boron nitride powder to orient along the magnetic power line in a magnetic field, and attained the present invention.
Namely, the present invention concerns a heat conductive mold characterized by that boron nitride powder is field oriented in a constant direction in polymer, a manufacturing method of heat conductive mold characterized by that boron nitride powder is field oriented in a constant direction in a composition by impressing magnetic field to a polymer component including boron nitride powder, and a manufacturing method of heat conductive mold characterized by that boron nitride powder is field oriented in a constant direction in a composition by impressing magnetic field to a liquid polymer component including boron nitride powder and solvent, and set after having removed the solvent.
Boron nitride powder used in the present invention is not particularly specified as for the kind of crystalline system, shape or size of powder particle, aggregation rate of powder particle, or their distribution. Concerning the crystalline system, boron nitride powder of hexagonal system, cubic system or other structures can be used. Particularly, highly crystalline boron nitride powder of hexagonal system or cubic system is preferable, because of its excellent thermal conductivity.
The particle form of boron nitride powder is not limited to flake form or flat form, but also various other forms of boron nitride powder, such as granular, massive, spherical, fiber, whisker form boron nitride powder, or ground product thereof can be used. The particle diameter of boron nitride powder is not specified; however, individual average primary diameter in the range of 0.01xcx9c100 xcexcm, and more preferably, in the range of 1xcx9c50 xcexcm can be used. Under 0.01 xcexcm, it is difficult to charge in quantity, and boron nitride powder larger than 100 xcexcm is difficult to produce, and disadvantageous in terms of price. As for the flake form boron nitride powder, it is practical to use within the range of 1xcx9c160 xcexcm in its maximum diameter, because it can easily be blended with polymer and field oriented. Further, boron nitride powder having a structure where primary particles are aggregated can be used.
In particular, the present invention is basically different from a conventional manufacturing method of mechanical orientation using boron nitride powder an-isotropic shape and is hardly influenced by the boron nitride powder shape, because it can be field oriented in a way to increase the heat conductivity using the magnetic anisotropy proper to the boron nitride powder.
The quantity of boron nitride powder to be contained in polymer is preferably 20xcx9c400 weight parts to 100 weight parts of polymer. Less than 20 weight parts, the improvement effect of heat conductivity is small, while the content more than 400 weight parts increases the composition viscosity, reduces the fluidity, making the molding difficult and bubble inclusion inevitable, so it is not appropriate. More preferably, boron nitride powder is added by 30xcx9c300 weight parts, and still preferably, by 40xcx9c250 weight parts. Higher concentrations may also be obtained by using boron nitride powders of different particle diameter, or by surface treatment.
The kind of polymer used for the present invention is not particularly limited. According to the shape, hardness, mechanical nature, thermal nature, electric nature, durability, reliability or other required performances, thermoplastic resins, thermoplastic elastomers, setting resins, reticulated rubbers, or the like can be selected. Polymer used for charging boron nitride powder at a high concentration, polymers and polymer precursors presenting low viscosity in liquid or melt state. Also, it is preferable to reduce the viscosity of polymers or polymer precursors by dissolving with solvent, in order to increase the concentration of boron nitride powder, or to accelerate the field orientation of boron nitride powder in the magnetic field atmosphere.
Thermoplastic resins or thermoplastic elastomers used as polymer include polyethylene, polypropylene, ethylene propylene copolymer or other ethylene xcex1 olefin copolymer, polymethylpentene, PVC, polyvinylidene chloride, polyvinyl acetate, ethylene vinylacetate copolymer, polyvinyl alcohol, polyvinylacetal, polyvinylidene fluoride and polytetrafluoroethylene or other fluoric resins, polyethylene terephthalate, polystyrene, polyacrylonitrile, styrene acrylonitrile copolymer, ABS resin, polyphenylene ether and degenerated PPE resin, aliphatic and aromatic polyamides, polyimide, polyamide-imide, polymethacrylic acid and its methylester or other polymethacrylic acid esters, polyacrylic acids, polycarbonate, polyphenylene sulfide, plysulfone, polyether sulfone, polyether nitrite, polyether ketone, plyketone, liquid crystal polymer, silicone resin, ionomer or other thermoplastic resins, styrene butadiene or styrene isoprene bloc copolymer and their hydrogenated polymer and styrene base thermoplastic elastomers, olefin base thermoplastic elastomers, PVC base thermoplastic elastomers, polyester base thermoplastic elastomers, polyurethane base thermoplastic elastomers, polyamide base thermoplastic elastomers, or other thermoplastic elastomers.
Thermosetting resins and reticulated rubbers include epoxy, polyimide, bismuth imide, benzocyclo butene, phenol, unsaturated polyester, diallyl phtalate, silicone, polyurethane, polyimide silicone, thermosetting type polyphenylene, ether resin and degenerated PPE resin, natural rubber, butadiene rubber, isoprene rubber, styrene butadiene copolymer rubber, nitrite rubber, hydrogenated nitrite rubber, chloroprene, ethylene propylene rubber, chlorinated polyethylene, chlorosulphonated polyethylene, butyl rubber and butyl rubber halide, fluoric rubber, urethane rubber, silicone rubber or other reticulated rubber.
The heat conductive mold of the present invention uses preferably, at least one of these polymers selected from silicone rubber, epoxy, polyurethane, unsaturated polyester, polyimide, bismuth imide, benzocyclobutene, fluoric resin, and polyphenylene ether resin, and more preferably, at least one of these polymers selected from silicone rubber, epoxy, polyimide and polyurethane in terms of heat resistance, and electric reliability. Moreover, these polymers can be a low viscosity liquid for blending with boron nitride powder and can reduce the viscosity when heat melted, and when magnetic field is impressed, boron nitride powder is oriented easily.
For wiring board application or the like requiring low dielectric constant, dielectric tangent and characteristics in high frequency range, fluoric resin or thermosetting type polyphenylene ether resin or degenerated PPE resin, polyolefin base resin are preferable. Further, polymer alloy made of a plurality of polymers selected from these polymers may also be used. The reticulation method of thermosetting resin or reticulated rubber is not limited to thermosetting, but polymers by publicly known reticulation methods such as photo-setting, hygro-setting, or the like may also be used.
The heat conductive mold of the present invention may be used with a small amount of other heat conductive filler of spherical, powder, fiber, needle, flake or whisker form filler made of highly conductive aluminum oxide, aluminum nitride, zinc oxide, silicon carbide, aluminum hydroxide or other metal oxides, metal nitrides, metal carbides, metal hydroxides or metals, alloys, carbon, graphite, and diamond.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.